Electrodes are produced in a vast array of shapes, configurations and constructions. However, all are essentially adapted to achieve the basic function of providing a potential difference within an electrolyte. It is conventionally considered that a major functionality of an electrode is to donate or receive electrons to or from an electrolyte to which it is exposed. Given these functions, electrodes must be electrically conductive, and are typically fabricated from a metal, graphite or semiconductor material.
The present invention is concerned with electrodes that are useful in methods for the treatment of water to reduce levels of organic compounds, infectious agents, heavy metals and the like. Common water contaminants include arsenic, asbestos, barium, bacteria, cadmium, chloradane, chlorine, chromium, copper Cryptosporidium, cyanide fluoride, Giardia, hydrogen sulphide, manganese, mercury, nitrates, nitrites, PCB, radium, radon, sulphate, toxaphene, trihalomethanes, viruses, volatile organic compounds, and zinc. It is known that certain contaminants in water may be precipitated or otherwise inactivated by the application of electric currents to water however such methods are not without problems.
The application of an electric current may in certain situations improve the quality of water by increasing levels of oxygenation. Such processes typically involve the direct and indirect oxidation of organic or inorganic compounds in aqueous solutions using catalytic electrodes. These processes can be used to lower BOD, COD and TOC in wastewater, or for the elimination of specific organic compounds. COD (Chemical Oxygen Demand) is the total measurement of all chemicals in the water that can be oxidized. TOC (Total Organic Carbon) is the measurement of organic carbon species. BOD (Biochemical Oxygen Demand) measures the amount of food (or organic carbon species) that are capable of oxidation by bacteria.
Traditionally, the electrolytic treatment of water often involves oxidizing organic compounds in an electrochemical cell both directly at the surface of a catalytic electrode and indirectly by oxidizing chemicals in solution. These treatments employ electricity as the main reactant and the addition of other chemicals is not required unless the solution conductivity is extremely low. In some cases the organic compounds can be converted to carbon dioxide and in many other cases to compounds that are more easily treated by biological processes.
The present invention is also concerned with electrodes useful in metallurgy, and particularly electrometallurgical reductive processes to produce pure metals from metallic compounds. One process that is well known in the art of metallurgy is the electro winning of gold. When two electrodes (cathode and anode) are placed in a solution containing gold ions and an electric current is passed between them, the pure metal is deposited on the negative electrode. An electrolyte, and a current density, is generally chosen that gives dense, compact electrodeposits, and some additives could be included in the electrolyte to further improve product quality. Usually cathodes used in the electro winning of gold are composed of steel wool and the anodes are stainless steel. Typically, the steel wool cathodes become fouled readily.
The electrolysis of water to produce hydrogen and oxygen is also an economically important process utilizing electrode technology. Other applications of electrolytic processes include the production of chlorine, sodium hydroxide, sodium chlorate, potassium chlorate and trifluoroacetic acid. In these applications, electrodes are typically of a basic rod or plate geometry.
Electrodes may also be used to apply electric fields to microorganisms such as algae for the purpose of altering biological characteristics such as permeability, buoyancy and growth rates. The growth of algae on an industrial scale is of significant economic importance in the production of commodities such as animal feed and biofuels.
While the above processes are driven by the application of an electric potential across the anode and cathode of the electrolytic process, the present invention is also concerned with electrodes used without directly applying a current to the electrolytic circuit. For example, a low current potential difference can drive additional ionic electron exchanges.
Methods and systems utilizing electrodes of the prior art have a number of problems, manifesting in the form of inefficiencies and relatively high power requirements. Relevant to those problems it has been estimated that around 4% of all electricity consumed in the United States goes toward the treatment of water. A large proportion of this energy is consumed in the aeration and reticulation of water. Further problems in the prior art include slow reaction rates, low yields of desired products, high levels of undesirable by products, insufficient extent of reaction, electrode fouling, and the like. It is an aspect of the present invention to overcome or alleviate one or more of the problems of the prior art to provide an improved electrode apparatus, and also methods and systems utilizing the improved electrodes.
A reference herein to a patent document or other matter which is given as prior art is not to be taken as an admission that that document or matter was known or that the information it contains was part of the common general knowledge as at the priority date of any of the claims.
Any feature or combination of features described herein are included within the scope of the present invention provided that the features included in any such combination are not mutually inconsistent as will he apparent from the context, this specification, and the knowledge of one of ordinary skill in the art. Additional advantages and aspects of the present invention are apparent in the following detailed description and claims.